Birds and reptiles commonly present with clinical illness related to liver disease. Biochemical tests, such as serum enzyme activities and bile acid concentrations, have been used for the antemortem diagnosis of liver disease in birds and reptiles, but these tests have clinical limitations.
In mammals, bilirubin quantitation is used to assess increased erythrocytic destruction and cholestasis. Hyperbilirubinemia is often observed in liver and hemolytic diseases. Therefore, total, conjugated, and unconjugated serum bilirubin concentrations and the presence or absence of bilirubinuria are used routinely in mammals as screening tests for hepatic function or extrahepatic disease. Liver diseases associated with hepatocellular swelling, hepatic fibrosis, hepatic inflammation or extrahepatic diseases resulting in red cell hemolysis, bile duct inflammation or obstruction may cause hyperbilirubinuria and bilirubinuria. The measurement of conjugated bilirubin in urine is of value in mammals because bilirubinuria often precedes the onset of hyperbilirubinemia. Measuring the serum concentrations of conjugated and unconjugated bilirubin can aid in differentiating extrahepatic from intrahepatic disease in mammals.
Birds and reptiles lack biliverdin reductase, the enzyme responsible for conversion of biliverdin to bilirubin; therefore, they do not produce bilirubin. In birds and reptiles, biliverdin (not bilirubin) is the waste product of hemoglobin destruction. Since bilirubin is not usually present in avian and reptile serum and urine, its measurement is not useful in evaluating liver disease or hemolytic disease in birds. The majority of biliverdin is excreted in an unconjugated form into the bile. Blood biliverdin concentration increases when hepatic regurgitation due to decreased function or biliary obstruction occurs, resulting in the typical green discoloration of plasma or urine.
The present invention provides a biochemical assay to quantitate the biliverdin present in plasma, serum or biological fluids collected from birds and reptiles. This test will prove of benefit as an adjunct to serum enzyme activities and bile acid concentrations in evaluating intra- and extrahepatic diseases in birds and reptiles.